CAPE CANAVERAL, Fla. — NASA has quietly extended its current partnership agreements with two of the three companies developing space taxis to fly astronauts to and from the international space station, documents posted on NASA’s website show.

Both Space Exploration Technologies Corp. and Sierra Nevada Corp. now have until March 2015 to complete milestones specified in their Commercial Crew Integrated Capability (CCiCap) contracts, which began in August 2012. The agreements previously were slated to end on Aug. 31, 2014.

An amendment signed by William Gerstenmaier, NASA’s associate administrator for human exploration and operations, on May 16 gives SpaceX until March 31, 2015, to complete the 14th and final milestone under its $440 million CCiCap agreement — a pad abort test of its Dragon capsule. The test originally was planned for April 2014.

On May 19, Gerstenmaier signed a similar amendment to Sierra Nevada’s $212.5 million CCiCap award to extend work associated with flight tests of the company’s Dream Chaser engineering test article until March 31, 2015.

NASA’s third Commercial Crew partner, Boeing, is on track to complete all its milestones, worth a combined $460 million, by the end of August, NASA spokeswoman Stephanie Martin wrote in an email to SpaceNews.

This is the second time NASA has extended the CCiCap agreements; last August the agency announced it was giving Boeing, Sierra Nevada and SpaceX an additional three months and a combined $55 million to tackle a handful of optional risk-reduction efforts.

Boeing, SpaceX and Sierra Nevada are vying for additional funding under the fourth and final round of the program. NASA expects to award one or more Commercial Crew Transportation Capability (CCtCap) contracts this summer.